Articulating spinal fixation rod and system

ABSTRACT

The present invention relates generally to systems and methods for aligning and implanting orthopedic fixation or stabilization implants within the body. In one embodiment, the system includes at least two bone anchors, at least one of which is provided with a transverse portal and a locking member. In one aspect, the system also includes at least one linkage rod, for linking two or more bone anchors through their respective locking members. The linking rod may include at least one angularly adjustable joint, which may be fixed by actuating the locking member. The bone anchors and the linkage rod may be locked into place to form a spinal fusion or fixation prosthesis.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to medical devices and, moreparticularly, to systems for aligning and implanting orthopedic fixationor stabilization implants within the body. In one application, thepresent invention relates to minimally invasive procedures and devicesfor implanting posterior instrumentation.

2. Description of the Related Art

The human vertebrae and associated connective elements are subject to avariety of diseases and conditions which cause pain and disability.Among these diseases and conditions are spondylosis, spondylolisthesis,vertebral instability, spinal stenosis and degenerated, herniated, ordegenerated and herniated intervertebral discs. Additionally, thevertebrae and associated connective elements are subject to injuries,including fractures and torn ligaments and surgical manipulations,including laminectomies.

The pain and disability related to these diseases, conditions, injuriesand manipulations often result from the displacement of all or part of avertebra from the remainder of the vertebral column. A variety ofmethods have been developed to restore the displaced vertebrae orportions of displaced vertebrae to their normal position and to fix themwithin the vertebral column. For example, open reduction with screwfixation is one currently used method. The surgical procedure ofattaching two or more parts of a bone with pins, screws, rods and platesrequires an incision into the tissue surrounding the bone and thedrilling of one or more holes through the bone parts to be joined. Dueto the significant variation in bone size, configuration, and loadrequirements, a wide variety of bone fixation devices have beendeveloped in the prior art. In general, the current standard of carerelies upon a variety of metal wires, screws, rods, plates and clamps tostabilize the bone fragments during the healing or fusing process. Thesemethods, however, are associated with a variety of disadvantages, suchas morbidity, high costs, lengthy in-patient hospital stays and the painassociated with open procedures.

Therefore, devices and methods are needed for repositioning and fixingdisplaced vertebrae or portions of displaced vertebrae which cause lesspain and potential complications. Preferably, the devices areimplantable through a minimally invasive procedure.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a system isprovided for the minimally invasive implantation of posterior fixationhardware. The system generally includes at least two bone anchors withtransverse portals and locking members. The system also generallyincludes a linking rod for linking two or more bone anchors throughtheir respective portals. The rod is provided with at least oneangularly adjustable joint. In many clinical situations, the rod isprovided with more than one angularly adjustable joint. The system mayalso include a driver for inserting the bone anchor into a bone andlocking the angularly adjustable joint with the locking member. In oneembodiment, an insertion tool is provided for the insertion of thelinkage rod. The bone anchors, the linkage rod and the joints may befixed by the locking of the locking members on the bone anchors, tosubcutaneously form a prosthesis.

In another aspect of the invention, an implantable fixation rodcomprises a first segment, having a proximal end and a distal end and asecond segment, having a proximal end and a distal end. A joint ispositioned between the first segment and the second segment. The jointis convertable between a first state in which the first and secondsegments are movable with respect to each other, and a second state inwhich the first and second segments are fixed with respect to eachother.

In another aspect of the present invention, a method is provided for theminimally invasive implantation of posterior fixation hardware. In oneembodiment, the method comprises the insertion of a first bone anchor,having a locking member and a transverse portal into a first vertebralbody. A second bone anchor, having a locking member and a transverseportal, is inserted into a second vertebral body. The first and secondvertebral bodies may be adjacent to each other, or separated by one ormore other vertebral body or bodies. A linkage rod with at least oneangularly adjustable joint is inserted through the portals of both boneanchors. The locking member of each bone anchor is then locked, fixingthe position of at least one of the angularly adjustable joints, andsecuring the linkage rod within the bone anchor, to form a prosthesis.

In accordance with another embodiment of the present invention, themethod further comprises the insertion of another bone anchor with atransverse portal and a locking member into another vertebral body. Thislatter vertebral body may be adjacent to either or both of the first andsecond vertebral bodies, or separated from both the first and secondvertebral bodies. The linkage rod is inserted through the transverseportals of the bone anchors to form the prosthesis.

In accordance with another embodiment of the present invention, themethod additionally includes the placement of one or more guide wires. Aguide wire may be inserted into a bone to define a path for theinsertion of a bone anchor. Another guide wire may be threaded throughthe portals of two or more bone anchors, to guide the insertion of thelinkage rod.

In any of the foregoing systems and methods, the guide wire may bereplaced or supplemented by a flexible guide tube. In suchimplementations of the invention, the bone anchor and/or the linkage rodmay be advanced through the interior of the guide tube.

Further features and advantages of the present invention will becomeapparent to those skilled in the art in view of the detailed descriptionof preferred embodiments which follows, when considered together withthe attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overview of a system for minimally invasive posteriorspinal fixation according to one embodiment of the present invention.

FIG. 2 is an exploded view of the bone anchor and the driver of FIG. 1.

FIG. 2A is an enlarged view of the circled area in FIG. 2.

FIG. 2B illustrates a locking cap and its complementary inner adapteraccording to yet another embodiment.

FIG. 2C illustrates a connector, a locking cap and its complementaryinner adapter according to yet another embodiment.

FIG. 2D illustrates an angularly adjustable connector with rotationlimits according to another embodiment.

FIG. 2E is a cross-sectional view of an angularly adjustable connectorwith rotation limits positioned within a head of a bone anchor accordingto another embodiment.

FIGS. 2F–2H illustrate another embodiment of a connector.

FIGS. 2I–2L illustrate another embodiment of a connector.

FIG. 3 is a side view of view of the system for minimally invasiveposterior spinal fixation illustrated in FIG. 1, with the fixation roddetached from its insertion tool.

FIG. 3A is an unassembled side view of the fixation rod of FIG. 3.

FIG. 3B is an assembled side view of a portion of the fixation rod ofFIG. 3 showing the range of angular adjustment.

FIG. 3C is an assembled top view of a portion of the fixation rod ofFIG. 3B showing the range of angular adjustment.

FIG. 4 is a side view of another embodiment of a system for minimallyinvasive posterior spinal fixation illustrated, with the fixation roddetached from its insertion tool.

FIG. 4A is another view of the system of FIG. 4.

FIG. 4B is an unassembled side view of the fixation rod of FIG. 4.

FIG. 4C is a side view of another embodiment of a system for minimallyinvasive posterior spinal fixation illustrated, with the fixation roddetached from its insertion tool.

FIG. 5 is another view of the system for minimally invasive posteriorspinal fixation illustrated in FIG. 1, with the linkage rod detachedfrom its insertion tool.

FIG. 5A is an enlarged view of the circled area in FIG. 4.

FIG. 6 is another view of the insertion tool of the system for minimallyinvasive posterior spinal fixation illustrated in FIG. 1.

FIGS. 7–12 illustrate the use of positioning tools to position a guidewire into a vertebral body.

FIGS. 13–14 illustrate the use of a dilation balloon catheter to dilatea tissue tract.

FIGS. 15–20 illustrate the positioning of a sheath adjacent to avertebral body.

FIGS. 21–23 illustrate a drill used to create an opening in a vertebralbody to receive a bone anchor.

FIGS. 24–25 illustrate advancing a bone anchor over the wire towards avertebral body.

FIGS. 26–27 illustrate a bone anchor and the driver used to insert thebone anchor into a vertebral body.

FIGS. 28–31 illustrate the use of the driver to insert a bone anchorinto a vertebral body.

FIG. 32 illustrates two bone anchors positioned in two adjacentvertebral bodies.

FIG. 33 is a side elevational perspective view of a guidewire positionedthrough two adjacent bone anchors.

FIG. 34 illustrates an alignment device for positioning a guidewirethough a bone anchor in accordance with one aspect of the presentinvention.

FIG. 35 illustrates a flexible obtuator for positioning within thearcuate arm of the alignment device.

FIG. 36 illustrates a first alignment device coupled to first boneanchor, and a second alignment device coupled to a second bone anchor.

FIG. 37 illustrate a guidewire capture device, for positioning withinthe arcuate arm on an alignment device.

FIG. 38 illustrates the first and second alignment devices, with aguidewire advancing from the first alignment device towards the capturedevice carried by the second alignment device.

FIG. 39 is an illustration as in FIG. 38, after the guidewire hasentered the guidewire capture device and traversed the curved arm on thesecond alignment device.

FIG. 40 is a side view of a linkage rod positioned over a guidewire.

FIG. 41 is an illustration as in FIG. 32, with the linkage rodpositioned within the first and second bone anchors.

FIG. 42 is an illustration as in FIG. 32, with a driver in position tolock the first bone anchor to the linkage rod.

FIG. 43 is an illustration as in FIG. 32, with a portion of the drivertool proximally retracted.

FIG. 44 is an illustration as in FIG. 43, with the driver toolretracted, the first and second bone anchors locked onto the linkagerod.

FIG. 45 is an illustration as in FIG. 44, with the insertion tooldecoupled from the linkage rod.

FIG. 46 is an illustration as in FIG. 45, with the insertion tool andthe guidewire removed from the linkage rod, illustrating a formed inplace one level posterior fusion device in accordance with the presentinvention.

FIG. 47 is an illustration as in FIG. 45, showing a two level fusion orfixation device, percutaneously assembled in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although the application of the present invention will be disclosedprimarily in the context of a spinal fixation procedure, the systems andmethods disclosed herein are intended for use in a wide variety ofmedical applications where the minimally invasive implantation of anattachment, bulking, brace, support, fixation or other prosthesis may bedesirable. The systems and methods disclosed herein may find alsoutility in a variety of medical procedures where it is desirableintroduce an implant into the body in a flexible configuration andthereafter convert the implant to a substantially rigid configuration(e.g., splinting or stabilizing a broken or fractured bone).

One advantage of the prosthesis formation described in the variousembodiments of the present invention is the ability to access atreatment site through minimally invasive pathways, while allowing theformation of a relatively larger prosthesis at the treatment site. Inone embodiment, various components of a prosthesis are inserted into apatient through minimally invasive pathways, then joined to form asingle prosthesis. This is facilitated by providing a linkage rod withangularly adjustable joints, which provide leeway or angularadjustability as the linkage rod is threaded through a plurality of boneanchors. Afterwards, the joints in the linkage rod may be locked to fixor set the linkage rod in a desired configuration.

A corollary advantage of several embodiments is the ability to unlockand adjust joints in the linkage rod, to set the prosthesis in otherdesirable configurations during or even after its implantation andformation. The prosthesis may thus be adjusted in subsequent procedures.

The systems and methods for spinal fixation according to variousembodiments of the present invention minimize procedure morbidity byavoiding open surgical cutdowns or other invasive access procedures. Thebasic percutaneous access, bone screw construction and implantationmethods, and methods and structures for percutaneously positioning afixation rod across bone screws, all of which are useful in the practiceof the present invention, are disclosed in U.S. patent application Ser.No. 09/747,066, entitled Percutaneous Vertebral Fusion System, toTeitelbaum, filed Dec. 21, 2000; U.S. patent application Ser. No.09/943,636 to Shaolian et al., entitled Formable Orthopedic FixationSystem, filed Aug. 29, 2001; U.S. patent application Ser. No. 09/976,459to Teitelbaum et al., entitled Formable Orthopedic Fixation System withCross-Linking, filed Oct. 10, 2001; and U.S. patent application Ser. No.10/161,554 to Shaolian et al., entitled Formed in Place Fixation Systemwith Thermal Acceleration, filed May 31, 2002; U.S. patent applicationSer. No. 10/462,098, filed Jun. 13, 2003 and entitled System and Methodfor Minimally Invasive Posterior Fixation, the disclosures of all ofwhich are hereby incorporated in their entireties by reference herein.

An overview of a system for minimally invasive posterior spinal fixationaccording to one embodiment of the present invention is provided inFIG. 1. The system includes at least two and optionally three or four ormore bone anchors 100 and an articulating jointed linkage rod 200. InFIG. 1, the bone anchors are shown connected by the jointed linkage rod200. The system may also include a driver 150, shown engaging one of thebone anchors 100, and an insertion tool 250, shown connected to thelinkage rod 200. Although these components will be described primarilyin the context of a single linkage rod connected to two bone anchors, anormal fusion application will typically involve the implantation of twolinkage rods, each carried by two or more bone anchors, bilaterallysymmetrically mounted on the spine as is well understood in the art.

FIG. 2 shows an exploded view of the bone anchor 100 and the driver 150.The bone anchor 100 is provided with threads 102 by which it is screwedinto a vertebral body. A locking cap 106 is disposed within the head 108of the bone anchor 100.

The driver 150 comprises an outer adapter 152 concentrically arrangedaround an inner adapter 154. Either adapter may be freely rotated withrespect to the other. The outer adapter 152 is adapted to engage thehead 108, to screw the bone anchor 100 into a bone. The inner adapter154 is adapted to engage the locking cap 106, to secure the fixation rod200 within the head 108. In one embodiment, the hexagonal proximal end156 of the outer adapter 152 allows torque to be applied to the outeradapter 152 by means of a wrench, a spanner or another tool. Similarly,the hexagonal proximal end 158 of the inner adapter 154 allows torque tobe applied to the inner adapter 154.

Releasable, rotational engagement between the driver and the bone anchormay be accomplished in any of a variety of ways. In the illustratedembodiment, the distal end the inner adapter 154 is provided with atleast one surface for cooperating with a complimentary surface on theproximal end of the bone anchor 100, for transmitting torque from theinner adapter 154 to the bone anchor 100, to enable transmission oftorque from the inner adapter 154 to locking cap 106. Similarly, thedistal end of the outer adapter 152 is provided with at least onesurface for cooperating with a complimentary surface on the proximal endof the bone anchor 100, for transmitted torque from the outer adapter152 to the bone anchor 100 to enable credible engagement between thebone anchor 100 and the vertebral body.

In one embodiment, the bone anchor 100, its locking cap 106, and theinner adapter 154 are all provided with a central axial lumen throughwhich a guide wire 190 may pass.

FIG. 2A is an enlarged view of the circled area in FIG. 2, showing theproximal head 108 of the bone anchor 100 and the distal ends of theouter adapter 152 and the inner adapter 154. The locking cap 106 isshown outside the head 108.

A transverse portal 116 extends through the head 108 along an axisapproximately perpendicular to the central axis of the bone anchor 100.While the transverse portal 116 of the head 108 is illustrated ascircular, it may be of different shapes in other embodiments, dependingupon the cross sectional shape of the fixation rod (e.g. oval,elliptical, rectangular, square, etc.). The diameter of the transverseportal 116 is generally larger than the diameter of the correspondingportions of the fixation rod 200 such that before the locking cap 106 istightened at least a portion of the fixation rod 200 may be insertedthrough the portal 116. In the illustrated embodiment, the portal 116includes a race or groove 114 within the head 108. The groove 114 ispreferably configured to be slightly larger than the diameter of thecorresponding portions of the fixation rod 200 but yet have a smallerdiameter than the portal 116. In other embodiments, the groove 114 maybe eliminated from the transverse portal 116.

FIG. 2B is similar to FIG. 2A above, and illustrates an inner adapter154′ and a locking cap 106′ according to another embodiment. In oneembodiment, the inner adapter 154′ is provided with a Torx distal end158′ which is adapted to engage a complementary Torx opening 120′ at thetop of the locking cap 106′. Any of a variety of complementary surfacestructures may be used, as will be understood in the art in view of thedisclosure herein.

In yet another embodiment, the head 108 of bone anchor 100 may also beprovided with an angularly adjustable connector 104 as shown in FIG. 2C.The connector 104 may be disposed within the head 108 beneath thelocking cap 106. In one embodiment, the connector 104 is spherical withan aperture 110 extending therethrough, and a gap 112 in itscircumference, such that it is approximately C-shaped when viewed alongthe central axis of the aperture 110. The aperture 110 is adapted forthe insertion of the linkage rod (not shown), and has a diameterslightly larger than that of the linkage rod. One skilled in the artwill understand that the connector 104 can be provided in a variety ofsuitable shapes.

In one embodiment, the connector 104 is seated on the race or groove 114which may be provided in the head 108 as described above. In suchembodiments, the groove 114 is preferably provided with a complementarysurface to the spherical exterior surface of the connector 104. Theconnector 104 may rotate on any axis within the head 108 of the boneanchor (or bone screw) 100. The locking cap 106 may be threaded into thehead 108 to lock the connector 104 against the linkage rod 200, bycompressing the groove 114, fixing the connector 104 within the head108. The bottom of the locking cap 106 may be provided with a concavesurface (not shown) which is complementary to the spherical exteriorsurface of the connector 104.

While the aperture 110 of the connector 104 is illustrated as circular,they may be of different shapes in other embodiments, depending upon thecross sectional shape of the fixation rod (e.g. oval, elliptical,rectangular, square, etc.). The diameter of the transverse portal 116 isgenerally smaller than the outside diameter of the uncompressedconnector 104 but greater than the inside diameter of the aperture 110.Before the locking cap 106 is tightened, the connector 104 may rotate onany axis within the head 108 to accommodate different entrance anglesfor the fixation rod. Thus the central axis of the aperture 110 and thecentral axis of the transverse portal 116 may be coaxial or angularlyoffset.

In one embodiment, the threading of the locking cap 106 into the head108 compresses the connector 104, decreasing the width of the gap 112and reducing the cross sectional area of the aperture 110. This securesa linkage rod (not shown) extending through the transverse portal 116 ofthe bone anchor 100 within the aperture 110. The tightening of thelocking cap 106 into the head 108 also fixes the rotational position ofthe connector 104 within the head 108.

FIG. 2D illustrates an alternate connector 104′. Similar to theconnector 104 described above, the connector 104′ is provided with anaperture 110′ having a longitudinal axis and a gap 112′. The sphericalexterior surface of the connector 104′ is provided with one or two orthree or more surface structures such as projections or indentations111. The indentations 111 receive complementary surface structures suchas projections provided within the head 108 of the bone anchor 100 tolimit the degree of rotation of the connector 104′ within the head 108.For example, FIG. 2E illustrates an exemplary embodiment wherein thecomplementary surface structure comprises a pin 101 that may be laserwelded or otherwise coupled to or integrally formed with the screw head108. As described above, the pin 101 interacts with the indentation 111to limit the degree of rotation of the connector 104′ within the head108. In one specific embodiment, the connector 104′ is limited to about30 degrees of rotation on any axis within the head 108, from thelongitudinal axis through the transverse portal 116. In otherembodiments, the connector 104′ may be limited to a range of up to about60 degrees of rotation from the longitudinal axis. In one embodiment,the connector 104′ is limited to no more than about 5 degrees or about10 degrees of rotation on any axis from the longitudinal axis. Ingeneral, the rotation of the connector 104′ is limited such that theaperture will always be exposed through transverse portal 116 to thelinkage rod 200.

FIG. 2F illustrates a connector 104″ according to another embodiment.Similar to the connectors 104 and 104′ described above, the connector104″ is provided with an aperture 110″ and one or more compressible gaps112″. The gaps 112″ are provided with a compressible material whichcompresses when the locking cap 106′ tightens the connector 104″ againstthe groove 114 within the head 108. Compressible material, including anyof a variety of compressible polymeric materials known in the medicaldevice arts can be used according to several embodiments of the presentinvention. One skilled in the art will appreciate that other suitableflexible or compressible materials may also be used. In addition, any ofa variety of metal (stainless steel, titanium, etc.) connectors 104 maybe configured such that the aperture 110 is moveable from a first, largecross-section, for receiving a linkage rod 200 therethrough, to asecond, reduced cross section for locking the linkage rod 200 in place.This may be accomplished by providing opposing components forming theside wall of the connector 104 with any of a variety of interlockingstructures such as ramp and pawl ratchet structures, or sliding fitstructures which permit a reduction in the diameter in the aperture 110under compressive force from the locking cap 106.

In an alternate embodiment, portions or all of the connector 104comprise a compressible media such as an open cell foam, closed cellfoam or solid compressible material. Structures comprising polyethylene,PEEK, nylon, and other polymers known in the medical arts may beutilized, depending upon the construction and desired compressibility.In general, the combination of material and the structure of theconnector 104 is sufficient to allow angular adjustment of thelongitudinal axis of the aperture 110, to accommodate various entranceangles of the linkage rod 200. After the linkage rod 200 has beenpositioned within the aperture 110, rotational and/or axial movement ofa locking element such as locking cap 106 functions to both preventaxial movement of the linkage rod 200 within the aperture 110, as wellas prevent further angular adjustment of the longitudinal axis of theaperture 110 with respect to the longitudinal axis of the bone anchor100.

FIGS. 2G–2H illustrate the connector 104″, the aperture 110″, the gaps112″, and a compressible or foldable membrane or link 115 in greaterdetail. FIG. 2F is an isometric view of the connector 104″. FIG. 2G is afront plan view of the connector 104″ viewed along the central axis ofthe aperture 110″. FIG. 2H is the corresponding side plan view. In theembodiment illustrated in FIGS. 2F–2H, the compressible link is formedby grinding, laser etching, molding or otherwise forming a recess suchas a V-shaped channel 113 that leaves a thin link 115 which folds flatwhen the connector 104″ is compressed. One of ordinary skill in the artwill understand that compressible materials and structures can beprovided in a variety of suitable shapes and forms.

In one embodiment, the apertures 110′ and 110″ have a tendency to returnto their original diameters even after the connectors 104 and 104′,respectively, are compressed by the locking cap 106 against the groove114 within the head 108. This tendency results from the resiliency ofthe metal, alloy or other material used to make the connectors 104 and104′. The use of compressible material, such as V-shaped channels 113 inthe gaps 112″ of the connector 104″, reduces or eliminates this tendencyand may allow a linkage rod (not shown) to be more firmly secured withinthe aperture 110″. One skilled in the art will understand that theconnectors 104 and 104′ can be made from lower resiliency materialswhich can also reduce or eliminate the tendency of apertures 110′ and110″ to return to their original diameters.

FIGS. 2I–L illustrate another embodiment of a connector 104′″ accordingto another embodiment. In this embodiment, the connector 104′″ isprovided with an aperture 110 and an indentation 111 as described. A topportion of the connector 104′″ is provided with a compressible materialor foldable link 117, which in comprises a series V-shaped channelsformed into the body of the connector 104′″. In the illustratedarrangements, the channels comprise a series of 40 degree V-shapedchannels 119 formed on the outer surface of the connector 104′″ and 20degree V-shaped channels 121 on the inner surface of the connector104′″. In a similar manner, a foldable link 123 is provided on a lowerportion of the connector 104′″. In this embodiment, as the locking cap106 is tightened the top and bottom portions of the connector 104″ aredeformed and laterally depressed so as to secure the fixation rod withinthe aperture 110.

Further details and additional embodiments of a bone anchor utilizing aconnector 104 can be found in co-pending U.S. patent application Ser.No. 10/462,098, filed Jun. 13, 2003, and entitled System and Method forMinimally Invasive Posterior Fixation, which was incorporated byreference above.

As discussed above with reference to FIG. 2, in one embodiment, theouter adapter 152 is adapted to engage the head 108, and the inneradapter 154 is adapted to engage the locking cap 106. In the illustratedembodiment, projections 156 on the distal end of the outer adapter 152are adapted to engage complementary projections 118 on the head 108 ofthe bone anchor 100. The hexagonal distal end 158 of the inner adapter154 is adapted to engage a complementary hexagonal opening 120 at thetop of the locking cap 106.

Although specific interlocking relationships between the driver 150 andthe bone anchor 100 are illustrated herein, the present inventorscontemplate a variety of modifications. For example, the male-femalerelationship between the driver and the implant may be reversed, foreither or both of the inner adaptor 154 and outer adapter 152. Inaddition, each of the inner adapter 154 and outer adapter 152 isprovided with a surface structure for enabling rotational engagementwith a corresponding component on the implant. Although this may beconveniently executed using corresponding hexagonal male and femalecomponents, any of a variety of alternative structures may be utilizedin which a first surface on the inner adapter 154 or outer adapter 152cooperates with a second, complementary surface on the correspondingaspect of the bone anchor 100, for allowing rotational engagement,followed by axial decoupling.

With reference now to FIGS. 3 and 3A, the jointed fixation rod 200 willnow be described in more detail. The fixation rod 200 preferablyincludes a first segment 204, a second segment 206 and a central lumen202, which is configured to receive a guidewire as will be explained inmore detail below. The first and second segments 204, 206 are coupledtogether by an angularly adjustable joint 208 a.

As will be explained in more detail below, the fixation rod 200 may beprovided with one or more joints 208 a. The joints 208 a provide thefixation rod 200 with a degree of flexibility that allows the fixationrod 200 to travel through a nonlinear, disjointed and/or curved path.This is particularly advantageous for inserting the fixation rod 200through the transverse portals 116 of a plurality of bone anchors 100.For example, it is generally difficult to align the transverse portals116 of a plurality of bone anchors 100 with each other because thesurfaces of the spine are typically non-planar and non-uniform. As such,each bone anchor 100 may extend from the spine at a different angularorientation and/or height. It is particularly difficult to align theportals between an anchor positioned in the L5 vertebra and an anchorthe S1 vertebra (i.e. sacrum).

It is therefore difficult to thread a straight or even curved fixationrod through the transverse portals 116 of more than one bone anchor 100.In a non-minimally invasive procedure, the surgeon may measure thedegree of non-alignment between the bone anchors 100 and bend thefixation device and/or adjust the position of the bone anchor in thespine. However, in a minimally invasive procedure, such adjustments areimpractical because they cause prolonged expose of the patient and theuse to fluoroscopical radiation.

Although a particular configuration of an articulating joint will bedescribed in detail below, any of a variety of structures may beutilized in implementing the present invention. In general, theimplantable fixation rod will have at least a first segment and a secondsegment which are angularly adjustable with respect to each other whilethe rod is in a first state, and fixed with respect to each other whenthe rod is in a second state. This permits, for example, percutaneousintroduction to a treatment site within a patient along a nonlinear pathwhile the rod is in the first state. The rod may then be converted tothe second state such that it exhibits a sufficient rigidity to producethe desired clinical result. This may be rigid fixation of a first boneor bone fragment with respect to a second bone or bone fragment.

The first and second segments will generally be separated by aninterface, at which a first attachment or interface surface on a firstsegment is in contact with a second, complementary attachment orinterface surface on the second segment. One implementation of this typeof interface is a ball and socket type joint, described below. Anothertype of interface may be formed, for example, by a leaf spring typestructure, or other axial element structures, such as two or moregenerally axially extending elements which are moveable with respect toeach other to permit flexion but can be locked relative to each othersuch as by lateral compression.

The articulating joint can be transformed from the movable state to thefixed state in any of a variety of ways. One convenient manner offixation is responsive to lateral compression which may be applied, forexample by an axially movable component (e.g., a threaded shaft such asa set screw) carried by the bone anchor. Thus in a ball and socket typestructure where a male component fits within a complementary femalecomponent, a surface on the outer female component may be flexed orcompressed laterally inwardly against a complementary surface on themale component to provide fixation. Either or both complementarysurfaces may be provided with friction enhancing surface structures suchas ridges, roughening or micropitting, as will be appreciated by thoseof skill in the art in view of the disclosure herein.

With reference to FIGS. 3 and 3A, the joint 208 a comprises a firstsurface 210 formed on the first segment 204 and a second complementarysurface formed on the second segment 206. In the illustrated embodiment,the first surface comprises a socket or recess 214 and the secondsurface comprises a ball 220 so as to form of a ball joint between theadjacent ends of the first and second segments 204, 206. The firstsegment 204 includes a socket portion 210, which comprises a generallycylindrical outer surface 212 that is configured to extend within thetransverse portal 116 of the bone anchor 100. The proximal end of thesocket portion 210 includes the generally spherical socket or recess214. At least one gap 216 is provided in the socket portion 210. In theillustrated embodiment, the at least one gap 216 extends from one sideof the outer surface 212, through the central lumen 202 and to theopposite side of the outer surface 212 and therefore divides the socketportion 210 generally in half. Compression of the gap 216 reduces thecross-sectional diameter of the socket 214 and fixes the angularposition of the joint 208 a as will be explained in more detail below.

The socket portion 214 is configured to receive the ball 220 orspherical protrusion that is provided on the distal end of the secondsegment 206. In one embodiment, the ball 220 is configured such that itmay be press-fitted into the socket 214. That is, the socket 214 definesan opening 222 that in a relaxed state is smaller than the maximumdiameter of the ball 220. In this manner, as the ball 220 is insertedinto the socket 214, the gap 216 expands to increase the diameter of theopening 222 and allow insertion of the ball 220 into the socket 218.Preferably, once in place, axial movement of the ball 220 with respectto the socket 214 is limited while at least limited angular adjustmentof the ball 220 with respect to the socket 216 is permitted. This may beaccomplished by providing the socket 216 with a slightly larger diameterthan the ball 220 and/or configuring the joint 208 a such that thefriction between the ball 220 and the socket 214 permits angularadjustment. In this manner, the angular orientation between the firstand second segments 204, 206 may be adjusted.

In the illustrated embodiment, the second segment 206 may be adjusted toany of a variety of angular orientations defined within a cone having avertex v positioned generally at the center of the socket 214 and theball 220. The angle a (see FIGS. 3B and 3C) represents the angularadjustment between the two segments and is defined primarily by theinterference between the proximal end of the socket portion 204 and aneck 224 on the proximal end of the ball 220. This angle may beincreased by decreasing the diameter of the neck 224. It should beappreciated that the maximum angle adjustment between the longitudinalaxes b, c of the first and second segments is generally half of theangle a of the vertex.

Depending upon the environment of use, the angle a of the vertex ispreferably within the range of about 15 to 90 degrees and the angle abetween the longitudinal axis of the second segment 206 with respect tothe first segment 204 may be rotated to any angle orientation withinsuch cone. In one embodiment, the angle a of the vertex within the rangeof about 15 to 30 degrees for joints 208 positioned at the lumbar levelsand within the range of about 45 to 90 degrees for joints 208 positionedat the L5 and S1 levels. In another embodiment, in the lumbar levels,the rod 200 may be fixed (e.g., formed without joints) while in the L5and S1 levels the vertex of the joints 208 may be in the range of about45 to 90 degrees.

One skilled in the art will understand that in other embodiments theillustrated ball joint may be replaced with any of a variety of otherangularly adjustable structures such as hinges or other slidingstructures that provide angular adjustment. For example, the shape ofthe socket and/or the ball may be modified in several different ways andstill provide the angular adjustability described above. In oneparticular embodiment, the angular adjustability may be modified and/orlimited. This may be accomplished by providing spherical exteriorsurface of the ball 220 with one or two or three or more surfacestructures such as projections or indentations. The indentations receivecomplementary surface structures such as projections provided within thesocket 214 to limit the degree of rotation of the ball 220 within thesocket 214 and/or the plane through which angular orientation may beadjusted. For example, in one embodiment, the first and second segmentsmay be angularly adjusted only through one plane (e.g., a horizontalplane).

In the illustrated embodiment, the socket portion 210 is configured tofit within the transversal portal 116 within the head 108 (see FIGS.2–2B) or through the aperture 110 in the connector 104 (see FIG. 2C).The portal 116 or aperture 104 is preferably provided with acomplementary surface to the cylindrical exterior surface 212 of thesocket portion. 210 As the socket portion 210 is inserted through thehead 108, the angular orientation of the second segment 206 with respectto the first segment 204 may be adjusted as the ball 220 rotates withrespect to the socket 214. The locking cap 106 may be threaded into thehead 108 to lock the angular orientation between the first and secondsegments 204, 206, by acting against the outer surface of the socketportion 210 or the connector 105 and fixing the ball 220 within thesocket 214. The bottom of the locking cap 106 may be provided with aconcave surface (not shown) which is complementary to the sphericalexterior surface 212 of the socket portion 210 or the connector.

In one embodiment, the threading of the locking cap 106 into the head108 compresses the socket portion 210, decreasing the width of the gap216 and reducing the cross sectional area of the socket 214. Thissecures the ball 220 within the socket 214 and fixes the angularorientation of the first segment 204 with respect to the second segment206. In the embodiments which use a connector 104, the locking cap alsofixes the angular position of the connector 104 within the head 108. Insome embodiments, the socket 214 and/or the ball 220 may be roughened,etched (e.g., mechanical, electrical, photo, chemical etc.) and/orcoated with material to increase the friction between these components.In this manner, the locking force between the socket 214 and the ball220 may be enhanced. Such techniques may also be applied to theconnector 104 and the outer surface of the first segment 204.

In the illustrated embodiment, the locking cap 106 also fixes the axialposition of the socket portion 210 within the bone anchor 100. However,in modified embodiments this may be accomplished by a separate device(e.g., a set screw).

In general for lumbar applications, in the locked position, the fixationrod 200 will preferably exhibit a static compression within the range offrom about 120 to about 200 lbs., and, more preferably greater thanabout 150 lbs and the rod will preferably exhibit a static torsionwithin the range of from about 15 to about 25 inch pounds, and, morepreferably in excess of about 20 inch pounds. The rods will preferablyreach at least about 5 million cycles, at 5 Hz. In general for cervicalapplications, in the locked position, the fixation rod 200 willpreferably exhibit a static compression within the range of from about30 to about 100 lbs., and, more preferably greater than about 80 lbs andthe rod will preferably exhibit a static torsion within the range offrom about 10 to about 20 inch pounds, and, more preferably in excess ofabout 15 inch pounds. The rods will preferably reach at least about 5million cycles, at 5 Hz. Each of these parameters may be measured inaccordance with the protocols described in the American Society forTesting and Materials (ASTM) designation F 1717-96, a copy of which isincorporated in its entirety herein by reference.

As mentioned above, the socket portion 210 and the corresponding gap 216formed in the socket portion preferably have a length of approximately10 to 30 millimeters. This provides the joint 208 a with a working rangein which the locking cap 106 can be used to fix the angular orientationof the joint 208 a. That is, the locking cap 106 can be used to fix theangular orientation of the joint 208 a as long as a least a portion ofthe socket portion 210 is positioned in the head 108 such that thelocking cap 106 may compress the gap 216.

For a one level application, typically two bone anchors 100 are insertedinto adjacent vertebrae. In such an application, the fixation rod 200preferably includes two joints 208 a, 208 b. As shown, in FIG. 3A, thesecond joint 208 b may be formed between a proximal end of the secondsegment 206 and a distal end of a third or end segment 230. In theillustrated embodiment, the proximal end of the second segment 206includes a spherical protrusion or ball 220, which may be configured asdescribed above. The end segment 230 includes a socket portion 210configured as described above and including a socket 214 to receive theball 220 of the second segment 206.

As can be seen FIG. 3, the first segment 204 of the linkage rod 200 maybe provided with a tapered distal end 232. The tapered distal end 232may be machined and be an integral part of the segment 204, may bemolded integrally with the socket portion 210 or may be separatelyformed and attached to the linkage rod 200. In one implementation, thetapered end 232 may be a polymeric component such as nylon, HDPE, PEBAXor other materials known in the art. The tapered tip 232 facilitatesadvance of the linkage rod 200 through the transverse portal 116. Inother embodiments, the distal end 232 may be blunt or ball shaped tominimize the protruding portion of the rod 200 from the portal 116 ofthe distal most anchor 100. In certain application, such embodimentsadvantageously reduce interference between the distal end of the rod 200and the S1 body.

With continued reference to FIG. 3, the end segment 230 may include ahexagonal proximal end 234. The hexagonal proximal end 234 may beconnected to the insertion tool as will be explained in more detailbelow.

The length of the linkage rod 200 in a device intended for use in ahuman adult one level lumbar or lumbar-sacral fusion, will generally bein the range from about 30 mm to about 90 mm and have a generallycircular cross-section with an average diameter within the range ofabout 5.5 mm to about 9 mm. In such an embodiment, the first segment 204and the end segment 230 will generally have a length within the range offrom about 10 mm to about 40 mm. The gaps 216 will generally have widthwithin the range of about 0.5 mm to 1.5 mm and a length within the rangeof from about 9 mm to about 29 mm. The socket portions 210 willgenerally have a length within the range of from about 10 mm to about 30mm. The second segment 206 will generally have a length within the rangeof about 10 mm to about 10 mm. The socket 214 and the ball 220 may havea diameter within the range of about 5.0 mm to 7.0 mm.

In a two level application, three bone anchors 100 are typicallyinserted into adjacent vertebra. In such an application, the fixationrod 200′ preferably includes four joints 208 a, 208 b, 208 c, 208 d. SeeFIGS. 4, 4A and 4B. As shown, in FIG. 4B, the four joints 208 a–d may beprovided by adding a fourth or intermediate segment 238 and anadditional second segment 240, which is configured as described above.The immediate segment 240 may include two sockets 214 positioned at thedistal and proximal ends of the segment 240 and a gap 216 that extendsthrough the entire length of the segment 240. The outer surface 212 isconfigured to fit within a bone anchor (see FIG. 4A) such thattightening the locking cap 106 compresses both of the sockets 214 in theintermediate segment 238 and thereby fixes the corresponding joints 208b, 208 c.

A linkage rod 200′ in a two-level device intended for use in a humanadult lumbar or lumbar-sacral fusion will generally have a length withinthe range of from about 70 mm to about 120 mm and a generally circularcross-section with an average diameter within the range of about 5.0 mmto about 9.0 mm. In such an embodiment, the first segment 204 and endsegment 230 will generally have a length within the range of from about10 mm to about 40 mm. The gaps will 216 will generally have a lengthwithin the range of from about 9 mm to about 29 mm and the socketportions 210 will generally have a length within the range of from about10 mm to about 30 mm. The second and intermediate segments 206, 240 willgenerally have a length within the range of from about 10 mm to about 40mm. The socket 214 and the ball 220 may have a diameter within the rangeof about 50 mm to 7.0 mm.

In another embodiment of the linkage rod 200 intended for two levelfusion for use in the treatment of thoracic and cervical segments of thespine, the rod 200 has a length of about 100 mm to 240 mm and agenerally circular cross-section with an average diameter of in therange of from about 3 mm to about 4 mm. In such an embodiment, the firstsegment 204 and end segment 230 will generally have a length within therange of from about 10 mm to about 40 mm. The gaps will 216 willgenerally have a length within the range of from about 9 mm to about 29mm and the socket portions 216 will generally have a length within therange of from about 10 mm to about 30 mm. The second and intermediatesegments 206, 240 will generally have a length within the range of fromabout 10 mm to about 40 mm. The socket 214 and the ball 220 may have adiameter within the range of about 5 mm to 7 mm.

FIG. 4C illustrates a modified embodiment of the fixation rod 200″. Thisembodiment is particularly suited for a level two device for use insacral-lumbar fusion. In this embodiment, the rod 200″ includes at leastone joint 208 a, and preferably two joints 208 a, 208 b, between thedistal and intermediate bone anchors 100 while the fixation rod 200″ isfixed (i.e., formed without joints) between the intermediate andproximal anchors 100. As such, in this modified embodiment, the proximalor end portion 230′ may be elongated as compared to the embodiment ofFIG. 3 such that it can extend through the intermediate and proximalanchors 100. The end portion 230′ may be substantially straight,partially curved or curved depending upon the clinical application. Inthis embodiment, the locking cap 106 in the proximal anchor 100 merelysecures the rod 200″ within the transverse portal 116.

In the embodiments described above, the cross sectional area of the rod200, which may be expressed as a diameter in a circular cross sectionalimplementation, may be varied depending upon the desired structuralintegrity of the finished implant. The anchors 100 will have a diameterof in the range of from about 3.5 mm to about 4 mm and a length in therange from about 10 mm to about 55 mm.

In modified embodiments, the gaps 216 in the fixation rod 200 may beprovided with a compressible material which compresses when the lockingcap 106 tightens the cylindrical portion within the head 108.Compressible material, including any of a variety of compressiblepolymeric materials known in the medical device arts can be usedaccording to several embodiments of the present invention. One skilledin the art will appreciate that other suitable flexible or compressiblematerials may also be used. In addition, any of a variety of metal(stainless steel, titanium, etc.) connectors may be configured such thatthe socket 214 is moveable from a first, large cross-section, forallowing movement of the ball 220 therethrough, to a second, reducedcross section for locking the angular position of the ball 220. This maybe accomplished by providing opposing in the socket portion 210 any of avariety of interlocking structures such as ramp and pawl ratchetstructures, or sliding fit structures which permit a reduction in thediameter in the socket 214 under compressive force from the locking cap106.

In a modified embodiment, portions or all of the socket portion 210comprise a compressible media such as an open cell foam, closed cellfoam or solid compressible material. Structures comprising polyethylene,PEEK, nylon, and other polymers known in the medical arts may beutilized, depending upon the construction and desired compressibility.In general, the combination of material and the structure of the socket214 is sufficient to allow angular adjustment of the longitudinal axisof ball 220 and the socket 214 to provide the linkage rod 200 with anangularly adjustable joint 208. After the socket portion 210 has beenpositioned within the transverse portal 116, rotational and/or axialmovement of a locking element such as locking cap 106 functions to bothprevent axial movement of the linkage rod 200 within the aperture 116,as well as prevent further angular adjustment of the joint 208.

In one embodiment, the sockets 214 have a tendency to return to theiroriginal diameters even after the cylindrical portions 210,respectively, are compressed by the locking cap 106 within the head 108.This tendency results from the resiliency of the metal, alloy or othermaterial used to make the cylindrical. The use of compressible material,such as V-shaped channels in the gaps 216, reduces or eliminates thistendency and may allow a linkage rod 200 and the joint 208 to be morefirmly secured. One skilled in the art will understand that the sockets214 can be made from lower resiliency materials which can also reduce oreliminate the tendency of sockets 214 to return to their originaldiameters.

In FIG. 5, the linkage rod 200 is shown positioned within two adjacentbone anchors 100, and released from the insertion tool 250. Theinsertion tool 250 is provided for the insertion of the linkage rod 200into the bone anchors 100. The insertion tool 250 comprises an arm 252and a handle 254. In the illustrated embodiment, the arm 252 is curvedto facilitate insertion of the linkage rod 200 into the bone anchors 100within a patient along a curved tissue tract which passes through theaperture 110 of at least each of a first bone anchor and a second boneanchor. However, it should be appreciated that in modified embodiments,the arm 252 may be of a different shape (e.g., straight) and be insertedthrough a tract of a different shape.

A central control line 256 (shown mostly in phantom) such as a torquetransmission tube, rod or cable extends through an axial lumen of theinsertion tool 250, and terminates at a control such as a knob 258 atthe proximal end of the insertion tool 250. A screw (not shown) threadedinto a tunnel 260 extending along a radius of the knob 258 may be usedto secure the control line 256 within the knob 258. The control line 256is provided with a threaded distal tip 262. Rotating the knob 258 thusrotates the control line 256 and its threaded distal tip 262 to engageor disengage the linkage rod 200.

In one embodiment, both the linkage rod 200 and the control line 256 areprovided with a central axial lumen for the passage over a guide wire.

FIG. 5A is an enlarged view of the circled area in FIG. 5, showing thedistal end of the outer adapter 152, the bone anchor 100, the linkagerod 200, and the distal end of the arm 252 of the insertion tool. Thelinkage rod 200 is shown fixed within the head 108 of the bone anchor100.

As mentioned above, linkage rod 200 is provided with a hexagonalproximal end 234 adapted to engage a complementary hexagonal socket (notshown) in the distal end of the arm 252 of the insertion tool. In someembodiments, alternative complementary surface structures may beprovided on the linkage rod 200 and the arm 252 to rotationally fixtheir orientation with respect to one another. In the illustratedembodiment, the hexagonal proximal end 234 is provided with a dimple 235adapted to engage a complementary nub (not shown) within the hexagonalsocket (not shown) in the distal end of the arm 252 of the insertiontool. The dimple 235 and nub (not shown) fix the axial orientation ofthe linkage rod 200 with respect to the arm 252. The threaded distal tip262 of the control line 256 may be threaded into a complementarythreaded hole 237 in the hexagonal proximal end 234 of the linkage rod200, enabling the linkage rod 200 to be detachably secured to the arm252 of the insertion tool. The threaded distal tip 262 may be threadedinto the threaded hole 206 by rotating the knob (not shown) at theproximal end of the insertion tool. Unthreading the threaded distal tip262 from the threaded hole 206 allows the linkage rod 200 to be releasedfrom the insertion tool 250.

With continued reference to FIG. 5A, in the illustrated embodiment, theouter adapter 152 is provided with an opening 160 extending along adiameter for fluoroscopic or other visualization of the rotationalorientation of the outer adapter 152, to align the portal 116 of thebone anchor 100 engaged by the outer adapter 152. Towards this end, theaxis of the opening 160 is preferably arranged at a right angle to theaxis of the portal 116 as shown in FIG. 5A. To visualize the axialposition of the outer adapter 152 and the bone anchor 100, the inneradapter 154 may be temporarily retracted so that it does not block theopening 160. In another embodiment a translucent marker may be installedin opening 160 for fluoroscopic or other visualization of the outeradapter 152.

Alternatively, any of a variety of other indicium of the rotationalorientation of the bone anchor 100 may be provided. For example, thecomplementary surface structures between the proximal end of the boneanchor 100 and the distal end of the insertion tool 250 may beconfigured to only allow coupling between the two components in apredetermined rotational orientation. In this construction, visualindicia may be provided on a portion of the insertion tool 250 (e.g. “T”handle, painted or etched markings or other indicium) which remainsexternal to the patient, to allow direct visual observation of therotational orientation of the longitudinal axis of the transverse portal116.

FIG. 6 illustrates the described insertion tool from another angle. Theknob and its attached central cable have been removed for clarity. Thehexagonal socket 264 adapted to engage the hexagonal proximal end (notshown) of the linkage rod, as described above, is shown. The nub 266adapted to engage the dimple (not shown) on the hexagonal proximal end(not shown) of the linkage rod is also shown.

In several embodiments, the components of the bone anchor, the linkagerod, the driver, and the arm of the insertion tool may be made oftitanium, stainless steel or any other suitable metals, alloys, ormaterial. The handle of the insertion tool is preferably made of asuitable non-slip material. The selection of these materials for themanufacture of the components and devices described in the aboveembodiments would be known by those skilled in the art.

Methods for the minimally invasive implantation of posterior fixationhardware according to embodiments of the present invention are disclosedin the context of a spinal fixation procedure with reference to FIGS.7–47. Additional details concerning the method are disclosed in thecopending patent applications incorporated by reference previouslyherein. Although the methods and instruments of the present inventioncan be utilized in an open surgical procedure, the present invention isoptimized in the context of a percutaneous or minimally invasiveapproach. Thus, the method steps which follow and those disclosed in thecopending patent applications incorporated by reference herein areintended for use in a trans tissue approach. However, to simplify theillustrations, the soft tissue adjacent the treatment site is notillustrated in the drawings discussed below.

In FIGS. 7 and 8, a trocar 300 is inserted through a tissue tract andinto a vertebral body 310. The trocar 300 comprises a sharp-tipped rod308 (shown in FIG. 16) attached to a proximal or top half-handle 302.The sharp-tipped rod 308 is arranged concentrically within a cannula304, which is attached to the bottom half-handle 306 of the trocar 300.The top half-handle 302 and the bottom half-handle 306 of the trocar 300are screwed together for initial use, as shown in FIGS. 7–8. The trocar300 is inserted through the skin, muscle and other tissues of thepatient into the vertebral body 310.

FIG. 9 shows the bottom half-handle 306 with the attached cannula 304embedded in the vertebral body 310. The top half-handle (not shown) hasbeen unscrewed and set aside from the bottom half-handle 306. In FIG.10, a guide wire 312 is inserted into the vertebral body 310 via thebottom half-handle 306 and the cannula 304.

In FIG. 11, the bottom half-handle 306 and the cannula 304 are removedfrom the vertebral body 310. Preferably, the guide wire 312 remains inplace in the vertebral body 310.

FIG. 12 shows the guide wire 312 in the vertebral body 310 after thebottom half-handle 306 and the cannula 304 are removed.

FIGS. 13–14 show one embodiment of use in which an inflatable tissueexpander for enlarging the tissue tract is used. In FIG. 13, a ballooncatheter 314 carrying a balloon 316 is advanced over the guide wire 312towards the vertebral body 310. In FIG. 14, the balloon 316 is inflatedto dilate the tissues adjacent the access pathway to the vertebral body310. This provides an enlarged path for the insertion of a sheath asdescribed below.

In FIG. 15, a guide tube 322 is advanced over the guide wire 312 intothe vertebral body 310. As shown in FIG. 16, in one embodiment, theguide tube 322 may be approximately the same diameter as the cannula 304of the trocar 300, allowing the guide tube 322 to be inserted into theopening in the vertebral body 310 created earlier by the trocar 300. Theguide tube 322 acts as a stable rail over which a tapered dilationcylinder 324 may be advanced against the vertebral body 310.

In FIGS. 16–17, a tapered dilation cylinder 324 is advanced over theguide tube 322 against the vertebral body 310. In one embodiment, thetapered dilation cylinder 324 may be approximately the same diameter asthe inflated dilation balloon 316 discussed above with reference toFIGS. 13–14. The tapered dilation cylinder 324 is used to occupy thepath created by the dilation balloon, and facilitates the insertion of asheath. In an alternate sequence, the dilation cylinder 324 is providedwithout a tapered distal end, and is distally advanced into positiondirectly over the inflatable balloon.

In FIGS. 18–20, a sheath 320 is advanced over the tapered dilationcylinder 324 against the vertebral body 310. The sheath 320 occupies thepath created by the dilation balloon. Afterwards, the guide tube 322 andthe tapered dilation cylinder 324 are removed. As shown in FIG. 20, theguide wire 312 preferably remains in the vertebral body 310 after theplacement of the sheath 320.

In FIGS. 21–23, a drill 330 having a rotatable distal tip 332 isadvanced over the guide wire 312 and through the sheath 320. The drill330 drills an opening (not shown) in the vertebral body 310 adapted forthe insertion of a bone anchor 100. Afterwards, the drill 330 isremoved. In FIGS. 24–25, the bone anchor 100 is advanced over the guidewire 312 and through the sheath 320 towards the vertebral body 310.

In FIGS. 24 and 25, a bone anchor 100 is advanced over the wire 312 andthrough the sheath 320 into engagement with the vertebral body 310.Although the insertion tool 250 is not illustrated, the bone anchor 100may be coupled to the insertion tool 250 prior to the step of advancingthe bone anchor 100 into contact with the vertebral body 310.

FIGS. 26 and 27 show the outer adapter 152 and the inner adapter 154 ofthe driver 150, as well as a bone anchor 100, with the the locking cap106 disposed within the head 108 of the bone anchor 100. Theinterrelation of these components have been described in detail abovewith reference to FIGS. 2 and 2A. The outer adapter 152 illustrated inFIGS. 26–28 additionally comprises a pivot hole 153 which extend througha diameter of the outer adapter 152. The pivot hole 153 is adapted forthe attachment of a guide wire insertion device 400 described in furtherdetail below. In FIG. 28, these components are shown arranged over aguide wire 190.

In FIG. 28, the driver 150 (comprising the outer adapter 152 and theinner adapter 154 ) is advanced over the guide wire 312 until the driver150 engages the bone anchor 100. In FIGS. 29 and 30, torque is appliedto the outer adapter 152 to screw the bone anchor 100 into the vertebralbody 310. In FIG. 31, the driver 150 is removed, leaving the bone anchor100 in place, with the longitudinal axis of the portal 116 alignedapproximately parallel with the longitudinal axis of the spine. Thesheath 320, discussed above with reference to FIGS. 18–25, while notshown in the steps discussed with reference to FIGS. 28–31, maynonetheless be used to shield the driver from adjacent tissue in thesesteps, as will be understood by those skilled in the art.

In FIG. 32, a second bone anchor 340 has been inserted into anothervertebral body 350. While bone anchors 100 and 340 are shown insertedinto adjacent vertebral bodies 310 and 350, respectively, the system andmethods for minimally invasive spinal fixation according to theembodiments of the present invention are also applicable to nonadjacentvertebral bodies. For example, a first bone anchor may be positioned ina first vertebral body as has been described above. A second bone anchormay be positioned in a second vertebral body, spaced apart from thefirst vertebral body by one or more intervening third vertebral bodies.The first and second bone anchors may thereafter be connected by theimplantation of a linkage rod 200. Alternatively, a third bone anchormay be positioned in a third vertebral body, positioned in between thefirst and second vertebral bodies to produce, for example, a three levelfusion system as will be discussed.

Preferably, after the bone anchors are in place, a guidewire 368 (seeFIG. 33 is advanced through the transverse portals 118 of the of boneanchors 100 and 340. Various methods of inserting guide wires are knownin the art and the invention is not limited to an particular method.Instead, various methods and devices for inserting a guide wire known tothose skilled in the art may be used in accordance with the presentinvention.

FIGS. 34–40 illustrate a particularly advantageous guide wire insertiondevice 400 according to one embodiment. The guide wire insertion devicecomprises a handle 410 and a hollow access needle 450. The handle 410 isdetachably joined to the outer adapter 152 of the driver 150. The handle410 is forked at its proximal end 412. Each fork is provided with apivot pin 414, which engages the pivot hole 153 (FIG. 28) of the outeradapter 152. The forked proximal end 412 of the handle 410 may be spreadslightly to allow the pivot pins 414 to engage the pivot hole 153. Thehandle 410 swings on its pivot pins 414 at the pivot hole 153 of theouter adapter 152 of the driver 150 to insert the access needle 450through the transverse portal 116 of the bone anchor 100.

A hollow access needle 450 is attached to the distal end 416 of thehandle 410. In one embodiment, the access needle 450 is disposed withinan opening 418 at the distal end 416 of the handle 410. A screw (notshown) may be threaded through a screw hole 420 at the distal end 416 ofthe handle 410 to tighten the access needle 450 within the opening 418.The lengthwise position of the access needle 450 within the opening 418is therefore adjustable to allow the access needle 450 to be aimedthrough the transverse portal 116 of the bone anchor 100. In oneembodiment, the access needle 450 may be aimed such that it passesthrough the transverse portal 116 at a point lower (towards the threads102 in FIG. 2) than the center of the transverse portal 116 becauseobstructions encountered during the in vivo insertion of the accessneedle 450 may deflect the needle 450 towards the inside of itscurvature and the center of the transverse portal 116.

In several embodiments, the sharp, tapered distal end 452 of the accessneedle 450 terminates at an opening 454. In one embodiment, the accessneedle 450 is provided with threaded proximal end 456, the purpose ofwhich is described in further detail below.

FIG. 35 illustrates a flexible obturator 500 of the guide wire insertiondevice 400 according to one embodiment. The obturator 500 comprises atubing 502, a threaded cap 504 on its proximal end and a plug 506 on itsdistal end. The tubing 502 is sized such that it fits snugly within thehollow access needle 450 and occupies the length of its lumen. The cap504 can be made with a threaded luer connector which may be tightenedonto the threaded proximal end 456 of the access needle 450. The plug506 may be formed from an adhesive, for example, Loctite 3104, etc. Theobturator 500 occupies the lumen of the access needle 450, and minimizesthe collection of tissue or other matter within the access needle 450 asit is advanced through the patient.

FIG. 36 shows a first guide wire insertion device 400 joined to a firstouter adapter 152 engaging a first bone anchor 100 and a second guidewire insertion device 400′ joined to the outer adapter 152′ engaging asecond bone anchor 340. In one embodiment, both handles 410 and 410′ arepivoted with respect to outer adapters 152 and 152′ to advance accessneedles 450 and 450′ through the patient's tissues and towards thetransverse portals 116 of bone anchors 100 and 340, respectively. FIG.36 also shows an obturator 500 according to one embodiment beinginserted into the access needle 450 of the guide wire insertion device400 as described above with reference to FIG. 35. Preferably, theobturator 500 is inserted into the access needle 450 and threaded ontoits threaded proximal end 456 before the access needle 450 is insertedinto the patient. Likewise, another obturator 500 may be inserted intothe access needle 450′.

In one embodiment of the present invention, the guide wire insertiondevice 400 additionally comprises a guide wire snare or capture device530, illustrated in FIG. 37. The guide wire capture device 530 comprisesan inner tubing 532 located coaxially within an outer tubing 534. Theinner tubing 532 is provided with an inner half-cone 536 and the outertubing 534 is provided with an outer half cone 538. The inner half-cone536 may be furled and retracted within the outer tubing 534. Likewise,the outer half-cone 536 may be furled to ease its insertion into andnavigation through the lumen of the hollow access needle 450. Innerhalf-cone 536 may be rotationally oriented with respect to outerhalf-cone 538 to form the conical funnel 540 of the guide wire capturedevice 530, as illustrated in FIG. 38. When a guide wire contacts theconical funnel 540 of the guide wire capture device 530, the guide wireis directed into the lumen 542 of the inner tubing 532. The guide wirecapture device 530 also additionally comprises a handle 544 in theillustrated embodiment.

In FIG. 39, the access needle 450 has been advanced through thetransverse portal 116 of bone anchor 100, and access needle 450′ hasbeen advanced through the transverse portal 116 of bone anchor 340. Theguide wire capture device 530 is inserted through the lumen of theaccess needle 450, and its conical funnel 540 is deployed. A guide wire368 is inserted through the lumen of the access needle 450′ and advancedtowards the conical funnel 540 of the guide wire capture device 530.When the guide wire 368 contacts the conical funnel 540, the guide wire368 is directed into the lumen 542 of the inner tubing 532 of the guidewire capture device 530.

In FIG. 40, the guide wire 368 is advanced through the lumen 542 of theinner tubing 532 until it extends past the handle 544 of the guide wirecapture device 530 As mentioned above, various methods of insertingguide wires are known in the art and the invention is not limited to themethods disclosed herein. Instead, any method of inserting a guide wireknown to those skilled in the art may be used in accordance with thepresent invention. Following placement of the guide wire 368, the firstinsertion device 400 and second insertion device 400′ may be removed.

In a modified embodiment, only the first the guide wire insertion device400 may be used to insert the guidewire 368 through the first boneanchor 100. The guidewire 368 may thereafter be pushed throughsubsequent bone anchors and tissue using traditional techniques with orwithout the aid of the insertion device 400.

A flexible or curved bone drill (not shown) may be advanced along theguide wire 368 to clear a path between the transverse portals 116 ofbone anchors 100 and 340. In one embodiment, the bone drill arm carryingthe drill bit is provided with a certain degree of flexibility to allowit to travel along the arcuate, discontinuous and/or non-linear courseof the guide wire 368. The bone drill is removed from the guide wire 368after a path has been cleared between transverse portals 116 of boneanchors 100 and 340.

In FIG. 41, a linkage rod 200 and its insertion tool 250 are shownarranged over the guide wire 368. The linkage rod 200 and insertion tool250 are described above with reference to FIGS. 3–3A. The linkage rod200 and insertion tool 250 in the embodiment illustrated in FIG. 41 areprovided with slightly different indexing features than the linkage rodand insertion tool described with reference to FIGS. 3–3A. Referringagain to FIG. 41 the linkage rod 200 is provided with one or more bumps220 on its hexagonal proximal end 202. The bumps 220 are complementarywith one or more holes 280 at the distal end of the insertion tool 250.In FIG. 34, the linkage rod 200 is detached from the insertion tool 250.The attachment of the linkage rod 200 to the insertion tool 250 isdescribed above with reference to FIGS. 5 and 5A.

In FIG. 41, the insertion tool 250 is used to advance the linkage rod200 over the guide wire 368 towards the bone anchors 100 and 340. Whilethe linkage rod 200 is inserted from a rostral or sacral approach(tail-to-head) in the illustrated embodiment, it may also be insertedfrom a caudal approach (head-to-tail) in another embodiment.

In FIG. 42, the linkage rod 200 is inserted through the respectivetransverse portals 116 within bone anchors 100 and 340. As mentionedabove, the linkage rod is provided with one or more joints 208. Thejoints 208 provide the linkage rod 200 with a degree of flexibility. Assuch, even if the transverse portals 116 are not aligned the linkage rod200 can track over the non-linear, curved or disjoined path as definedby the guidewire 368 and extending between portals 116.

As shown in FIGS. 43–44, the inner adapter 154 of the driver 150 may beused to tighten the locking cap 106 within the bone anchor 340, fixingthe linkage rod 200 within the bone anchor 340 and fixing the angularrelationship of the joint 208, as described above with reference toFIGS. 2–3A and/or the connector 104. The outer adapter 152 of the driver150 engages the head of bone anchor 340 to prevent it from rotating asthe locking cap is tightened. The engagement between the bone anchor 340and the driver 150 is described above with reference to FIGS. 1–2A inthe context of bone anchor 100.

In FIG. 45, the driver 150 (comprising the outer adapter 152 and theinner adapter 154) is withdrawn from the bone anchor 340. The lockingcap 106 in the bone anchor 100 is similarly tightened, fixing thelinkage rod 200 within the bone anchor 100.

In FIG. 46, the insertion tool 250 is released from the linkage rod 200.The attachment and detachment of the linkage rod 200 to and from theinsertion tool 250 is discussed above with reference to FIGS. 5 and 5A.Afterwards, the driver 150, the sheath 320 and the guide wire 368 areremoved from the patient. As such, FIG. 46 illustrates thepercutaneously assembled in place prosthesis resulting from theprocedure described above, comprising the bone anchors 100, 340 and thelinkage rod 200.

FIG. 47 illustrates a three level prosthesis comprising an additionalbone anchor inserted into an additional adjacent vertebral body and thelinkage rod of FIGS. 4–4B, to provide a three level spinal fusion.

In one embodiment, the transverse portal 116 of the proximal bone anchoris provided with a proximal opening having a first diameter and distalopening having a second, smaller diameter. The outside diameter of theproximal segment 230 is dimensioned relative to the portal 116 such thatit can pass through the proximal opening on the transverse portal 116but cannot pass distally through the distal opening of the transverseportal 116. In this manner, the clinician can perceive tactile feedbackonce the proximal segment 230 has been distally advanced into positionwithin the head 108. This same construction can be utilized on thedistal bone anchor as well, such that distal advancement of the firstsegment through the transverse portal 116 is limited. In modifiedembodiments, the outside diameter of the first and proximal segments204, 230 may be tapered to achieve the result described above.

Not all of the steps described above are critical to the minimallyinvasive implantation of posterior fixation hardware. Accordingly, someof the described steps may be omitted or performed in an order differentfrom that disclosed. Further, additional steps may be contemplated bythose skilled in the art in view of the disclosure herein, withoutdeparting from the scope of the present invention. In addition, thespecific dimensions and angles mentioned above can be readily varieddepending upon the intended application, as will be apparent to those ofskill in the art in view of the disclosure herein.

The present inventors contemplate the interchangeability of andrecombination of various structural and method elements in the foregoingdescription. For example, the guidewire may be positioned throughportals of adjacent bone anchors utilizing either the proceduresdisclosed in the copending patent applications previously incorporatedby reference herein. As a further alternative, a tubular sleeve may beadvanced over the guidewire and through the portals on bone anchors 100,with the guidewire thereafter removed. The linkage rod 200 maythereafter be advanced through the tubular sleeve.

The various materials, methods and techniques described above provide anumber of ways to carry out the invention. Of course, it is to beunderstood that not necessarily all objectives or advantages describedmay be achieved in accordance with any particular embodiment describedherein. Thus, for example, those skilled in the art will recognize thatthe components of the system may be made and the methods may beperformed in a manner that achieves or optimizes one advantage or groupof advantages as taught herein without necessarily achieving otherobjectives or advantages as may be taught or suggested herein.

Although the present invention has been described in terms of certainpreferred embodiments, other embodiments of the invention includingvariations in dimensions, configuration and materials will be apparentto those of skill in the art in view of the disclosure herein. Inaddition, all features discussed in connection with any one embodimentherein can be readily adapted for use in other embodiments herein. Theuse of different terms or reference numerals for similar features indifferent embodiments does not imply differences other than those whichmay be expressly set forth. Accordingly, the present invention isintended to be described solely by reference to the appended claims, andnot limited to the preferred embodiments disclosed herein.

1. A prosthesis for minimally invasive posterior fixation, comprising: abone anchor having a head; a transverse portal extending throughopposing sidewalls of said head along an axis transverse to a centralaxis of said bone anchor, said opposing sidewalls being substantiallyclosed above said transverse portal; a first segment of a rod extendingthrough said transverse portal, said first segment defining a firstsurface; a second segment of a rod having a second complementarysurface; a joint formed at least in part by said first surface and saidsecond surface; and a locking cap which in response to lateral movementsecures said first segment within said portal and fixes the angularrelationship of the joint.
 2. The prosthesis of claim 1, wherein saidrod is adapted to be detachably secured to an insertion tool used toinsert said rod into said portal.
 3. The prosthesis of claim 1, furthercomprising a third segment of the rod, said third segment defining asocket for receiving a ball positioned on said second segment.
 4. Theprosthesis of claim 3, further comprising a second bone anchor having ahead, a transverse portal and a locking cap which in response to lateralmovement secures said third segment within the portal of the second boneanchor and fixes the angular relationship between the third and secondsegments.
 5. The prosthesis assembly of claim 4, wherein the thirdsegment is configured to be secured to an insertion tool used to insertsaid rod into said portals of said bone anchors.
 6. The prosthesis ofclaim 4, wherein said first segment, said second segment and said thirdsegment include a central lumen, which is configured such that saidfirst second and third segments can travel over a guidewire.
 7. Theprosthesis of claim 4, wherein the transverse portal of said second boneanchor is substantially closed with respect to a central axis of saidsecond bone anchor.
 8. The prosthesis of claim 7, wherein said firstsegment, said second segment and said third segment include a centrallumen, which is configured such that said first second and thirdsegments can travel over a guidewire.
 9. The prosthesis of claim 4,wherein said first segment has distal end and said transverse portal ofsaid second bone anchor is configured such that said distal end of saidfirst segment can be advanced entirely through said transverse portal ofsaid second bone anchor.
 10. The prosthesis of claim 1, wherein saidfirst segment and second segment include a central lumen, which isconfigured such that the first and second segments can be advanced overa guidewire.
 11. The prosthesis of claim 1, wherein said first segmenthas distal end and said transverse portal is configured such that saiddistal end of said first segment can be advanced through a first end ofsaid portal.
 12. The prosthesis of claim 1, wherein said first segmenthas distal end and said transverse portal is configured such that saiddistal end of said first segment can be advanced entirely through saidtransverse portal.
 13. A prosthesis for minimally invasive posteriorfixation, comprising: a bone anchor having a head; a transverse portalextending through said head along an axis transverse to a central axisof said bone anchor; a first segment of a rod extending through saidtransverse portal, said first segment defining a first surface; a secondsegment of a rod having a second complementary surface; a joint formedat least in part by said first surface and said second surface; and alocking cap which in response to lateral movement secures said firstsegment within said portal and fixes the angular relationship of thejoint; wherein said first segment further comprises at least onecompression gap.
 14. The prosthesis of claim 13, wherein said rod isadapted to be detachably secured to an insertion tool used to insertsaid rod into said portal.
 15. The prosthesis of claim 13, furthercomprising a third segment of the rod, said third segment defining asocket for receiving a ball positioned on said second segment.
 16. Theprosthesis of claim 15, further comprising a second bone anchor having ahead, a transverse portal and a locking cap which in response to lateralmovement secures said third segment within the portal of the second boneanchor and fixes the angular relationship between the third and secondsegments.
 17. The prosthesis assembly of claim 16, wherein the thirdsegment is configured to be secured to an insertion tool used to insertsaid rod into said portals of said bone anchors.
 18. The prosthesis ofclaim 13, wherein said rod includes a central lumen, which is configuredsuch that said rod can be advanced over a guidewire.
 19. The prosthesisof claim 13, wherein said first segment has distal end and saidtransverse portal is configured such that said distal end of said firstsegment can be advanced through a first end of said portal.
 20. Theprosthesis of claim 13, wherein said first segment has distal end andsaid transverse portal is configured such that said distal end of saidfirst segment can be advanced entirely through said transverse portal.21. A prosthesis for minimally invasive posterior fixation, comprising:a first bone anchor having a head and a transverse portal extendingthrough said head along an axis transverse to a central axis of saidfirst bone anchor; a second bone anchor having a head and a transverseportal extending through said head along an axis transverse to a centralaxis of said second bone anchor; a first segment of a rod extendingthrough said transverse portal of said first bone anchor, said firstsegment defining a first surface, said first segment being configuredsuch that it can be advanced entirely through said transverse portal ofsaid second bone anchor; a second segment of a rod having a secondcomplementary surface; a joint formed at least in part by said firstsurface and said second surface; and a locking cap that is configuredfor lateral movement within said head of said first bone anchor and isconfigured such that lateral movement within said head secures saidfirst segment within said portal and fixes the angular relationship ofthe joint.
 22. The prosthesis of claim 21, wherein said rod is adaptedto be detachably secured to an insertion tool used to insert said rodinto said portal.
 23. The prosthesis of claim 21, further comprising athird segment of the rod, said third segment defining a socket forreceiving a ball positioned on said second segment.
 24. The prosthesisof claim 23, further comprising a cap for the second bone anchor that inresponse to lateral movement secures said third segment within theportal of the second bone anchor and fixes the angular relationshipbetween the third and second segments.
 25. The prosthesis assembly ofclaim 24, wherein the third segment is configured to be secured to aninsertion tool used to insert said rod into said portals of said boneanchors.
 26. The prosthesis of claim 21, wherein said rod includes acentral lumen, which is configured such that the rod can be advancedover a guidewire.
 27. The prosthesis of claim 21, wherein said firstsegment has distal end and said transverse portal of said first boneanchor is configured such that said distal end of said first segment canbe advanced through a first end of said transverse portal of said firstbone anchor.
 28. The prosthesis of claim 21, wherein said first segmenthas distal end and said transverse portal is configured such that saiddistal end of said first segment can be advanced entirely through saidtransverse portal of said first bone anchor.
 29. A prosthesis forminimally invasive posterior fixation, comprising: a bone anchor havinga head; a transverse portal extending through said head along an axistransverse to a central axis of said bone anchor; a first segment of arod extending through said transverse portal, said first segmentdefining a first surface; a second segment of a rod having a secondcomplementary surface; a joint formed at least in part by said firstsurface and said second surface; means for securing said first segmentwithin said portal and fixing the angular relationship of the joint; anda guidewire lumen extending through said first and second segments ofthe rod.
 30. The prosthesis of claim 29, wherein said rod is adapted tobe detachably secured to an insertion tool used to insert said rod intosaid portal.
 31. The prosthesis of claim 29, wherein further comprisinga third segment of the rod, said third segment defining a socket forreceiving a ball positioned on said second segment.
 32. The prosthesisof claim 31, wherein said guidewire lumen extends through said thirdsegment
 33. The prosthesis assembly of claim 31, wherein the thirdsegment is configured to be secured to an insertion tool used to insertsaid rod into said portals of said bone anchors.
 34. A prosthesis forminimally invasive posterior fixation, comprising: a first bone anchorhaving a head and a transverse portal extending through said head alongan axis transverse to a central axis of said first bone anchor; a secondbone anchor having a head and a transverse portal extending through saidhead along an axis transverse to a central axis of said second boneanchor; a first segment of a rod extending through said transverseportal of said first bone anchor, said first segment defining a firstsurface; a second segment of a rod having a second complementarysurface; a joint formed at least in part by said first surface and saidsecond surface, said joint configured to allow an angular orientation ofsaid first and second segments to be adjusted within a cone having avertex located between said first and second bone anchors; and a lockingcap which in response to lateral movement secures said first segmentwithin said transverse portal of said first bone anchor and fixes theangular relationship of the joint.
 35. The prosthesis of claim 34,wherein said rod is adapted to be detachably secured to an insertiontool used to insert said rod into said portal.
 36. The prosthesis ofclaim 34, wherein further comprising a third segment of the rod, saidthird segment defining a socket for receiving a ball positioned on saidsecond segment.
 37. The prosthesis of claim 34, wherein said firstsegment and second segment include a central lumen, which is configuredsuch that the first and second segments can be advanced over aguidewire.
 38. The prosthesis of claim 34, wherein said first segment isconfigured such that it can be advanced entirely through said transverseport of said second bone anchor.